class Foo():
    # xxx = 444
    pass
class Bar1(Foo):
    # xxx = 333
    pass
class Bar2(Bar1):
    # xxx = 222
    pass

obj = Bar2()
# print(obj.xxx) # 222
# print(obj.xxx) # 333
# print(obj.xxx) # 444
# print(obj.xxx) # AttributeError: 'Bar2' object has no attribute 'xxx'
